It's hard to say for sure but I would guess that you actually have build errors so the build is failing and you actually running old output. The simple option is to open the 'bin' folder and delete the contents. If you do have build error then there's no old output to run so you'll be forced to fix them. If there are no build errors and it was just a glitch, which does seem to happen occasionally, then that will force new output to be created.